A technique is known which reduces frictional resistance of a hull by covering the bottom surface of a ship with an air bubble flow at the time of navigation.
Referring to FIG. 1, a hull frictional resistance reducing device described in JP 2008-143345A will be described. A gas room 2 is provided on the bow side in a bottom section 1 of a ship. The gas room 2 is formed in the width direction. The gas room 2 is divided into three gas rooms 2a in the width direction of the ship bottom section 1 by partitions 2b. Parts of the outer plate of the ship bottom corresponding to the gas rooms 2a are cut to form bottom openings 1a with no bottom plate. Each gas room 2a is connected with a compressor 4 through the gas supply pipe 3. In each gas room 2a, a baffle plate 6 is provided apart below from a connection opening of the gas supply pipe 3 in the top wall to receive a gaseous flow. A pair of gas holding boards 5 is provided from a bow section toward a stern section along the both sides of the ship bottom.
Because the baffle plate 6 receives a gas blown from the gas supply pipe 3 into the gas room 2a, the gas filling the gas room 2a is blown in an almost uniform condition from the bottom opening 1a into the water. In this way, it is possible to generate the air bubble flow which efficiently flows to the backward side along the ship bottom surface. Moreover, the outward flow of the air bubble flow into the hull sides is prevented by the gas holding boards 5. In this way, the hull frictional resistance is reduced.